As a substitute for breast milk to be administered to an infant not given breast milk with various causes or suffering from shortage of breast milk, a infant formula of which the only protein source is milk protein has been developed. Taking account of growth condition and constitution of infants, many food products for infants of which the only protein source is milk protein or processed milk protein have been developed. Examples of these products other than infant formula include follow-up formula for infants older than six months of age and protein hydrolyzed formula for infants having allergic constitution.
However, along with the fortification of nutrients necessary for the growth of infant and the modification of nutritional compositions closer to breast milk for the purpose of improving these products, it has been pointed out that stool of infants ingesting these products apparently differs from that of breast-fed infants. More specifically, in case of infants ingesting infant formula in which the iron is fortified to satisfy nutritional requirements of infants and the ratio of casein protein to whey protein is increased to a level similar to that of breast milk (i.e., the ratio of whey protein is increased), the stool color is known to be green with higher frequency (Journal of Pediatric Gastroenterology and Nutrition, Vol. 4, p. 771, 1985).
Similarly in case of infants having ingested protein hydrolyzed formula because of their allergic constitution, it is known that the stool color also become green with higher frequency (Pediatrics, Vol. 95, p. 50, 1995).
More recently, there has been developed a protein hydrolyzed formula in which all protein of the formula is appropriately hydrolyzed and which is expected to have a preventive effect of allergic diseases. The stool color of infants who ingest this product, is also tended to be green (Shokuhin Kogyo (The Food Industry), Vol. 38, No. 4, p.55, 1995).
These facts evidence that infant formula and various related products thereof have not as yet reached the level of breast milk in many aspects, and prompt improvement has been demanded.
With a view to solving the problem of green stool of infants, improvement of green stool by adding fruct-oligosaccharide (namely .beta.-2,1-fruct-oligosaccharide and/or .beta.-2,6'-fruct-oligosaccharide) with infant formula at a ratio of from 2 to 5% (by weight) is tried (Japanese Patent Provisional Publication No.266,937/91). According to the Publication No.266,937/91, even in infants having ingested infant formula added with fructo-oligosaccharide at a ratio of from 2 to 3% (by weight), the ratio of yellow stool is only up to a half (44 to 50%). Since the ratio of yellow stool among breast-fed infants surveyed as reference is at least 90%, presence of marked difference between the two cases is disclosed.
For the purpose of reducing stool odor and improving stool character such as color and hardness by means of improvement of intestinal condition, an invention covering an intestinal condition improving agent containing a mushroom extract alone or mushroom extract, a dietary fiber and/or oligosaccharide is disclosed (Japanese Patent Provisional Publication No.238,945/93), and as a concrete embodiment of this oligosaccharide, soy oligosaccharide is disclosed. In this Publication No.238,945/93, mushroom extract is an essential component, and it discloses that a synergism of the mushroom extract and oligosaccharide or dietary fiber cleans the intestinal condition and considerably improves odor, color, hardness and the like of stool.
On the other hand, raffinose (which is composed of glucose, galactose and fructose) is known to be contained in a certain amount in soybean formula mainly composed of soybean protein, together with stachyose as oligosaccharide resulting from the raw material (Journal of Dairy Research, Vol. 53, p. 293, 1986). Some of these products are popularly used in Europe and the United States, and in infants having ingested soybean formula, a high frequency of green stool is observed in spite of inclusion of raffinose (Pediatrics, Vol. 95, p. 50, 1995).
The most important differences between breast-fed and formula-fed infants are color and frequency of bowel movement. While in breast-fed infants, the frequency of stool presenting yellow color is high, and the daily frequency of bowel movement is also high, formula fed infants are known to show a high frequency of presenting green stool color and apparently lower daily frequency of bowel movement as compared with breast-fed ones (The Journal of Child Health, Vol. 43, p. 618, 1984). This problem of green stool is most frequently taken up in childcare consultation, and one of the most anxious matter of mothers, although this is not an indicator of morbid syndromes.
The phenomenon of green stool is thought to be due to the secretion ratio of bilirubin and biliverdin, which are bile pigments secreted from gallbladder, and to the alteration of those substances through the oxidative or reductive reactions occurred directly or indirectly in the intestine. Therefore, in an infant administered with infant formula containing large quantity of substances affecting oxidation and reduction of the contents in the intestine (iron, for example), the frequency of green stool becomes higher. It is furthermore known that, in such iron-fortified infant formula, if the ratio of whey protein in total protein is increased, stool tends to become green more frequently (Journal of Pediatric Gastroenterology and Nutrition, Vol. 4, p. 771, 1985).
The trials to improve the stool color of infants having ingested foods for infants other than breast milk to a level closer to that of breast-fed infants, have been unsuccessful, and there has been a demand for a food for infants which improves the stool color of sucking infants.